Poly(lactic acid) (PLA) is a promising bio-based polymer of high interest in additive manufacturing (AM). Its immanent brittleness makes it necessary to blend it with flexible polyester, such as poly(butylene succinate) (PBS). Blending PLA with PBS is an effective way to fine-tune the properties of neat polymers. However, the immiscibility between PLA and PBS polymers leads to their performance impairment and application limitations. Copolymers that work as plasticizers, compatibilizers, and nucleating agents for property improvement can be used as multifunctional additives for polymer blends. This work represents a copolymer, i.e., poly(lactide-co-butylene succinate) (PLA-co-PBS) with ratios 75-25 and 25-75. PLA/PBS blends with different mass ratios of 25/75, 50/50, and 75/25 were produced by dissolving all components (PLA, PBS, and PLA-co-PBS) in CHCl3 and casting them in a petri dish. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used to assess the changes in the phase structure of PLA/PBS blends. Tensile tests demonstrated the addition of PLA-co-PBS improved tensile strength and elastic modulus values for all blends. Synthesizing tunable PLA-co-PBS block copolymers as multifunctional compatibilizers could enhance miscibility, interface compatibility, and overall performance of PLA/PBS blends, surpassing traditional approaches and promising eco-friendly packaging and agricultural materials.